JP2020049483A - Exhaust gas purifying catalyst for internal combustion engine and exhaust gas purifying method using the same - Google Patents

Abstract

To provide an exhaust gas purifying catalyst for an internal combustion engine and an exhaust gas purifying method using the catalyst.SOLUTION: An exhaust gas purifying catalyst includes a carrier, a first catalyst layer on an upstream side, a second catalyst layer on a downstream side, and a third catalyst layer. An upstream side part of the third catalyst layer is present on the first catalyst layer. A downstream side part of the third catalyst layer is present on the second catalyst layer. An intermediate part between the upstream side part of the third catalyst layer and the downstream side part thereof is present between the first catalyst layer and the second catalyst layer.SELECTED DRAWING: None

Description

  The present invention relates to a catalyst for purifying exhaust gas of an internal combustion engine and a method for purifying exhaust gas using the catalyst. More specifically, the present invention relates to a purifying catalyst having a higher purifying performance than before and a method for purifying exhaust gas using the catalyst.

  More specifically, for example, the present invention relates to a catalyst which can be used even in an environment where exhaust gas of an internal combustion engine is exposed to a high temperature at a high temperature for a long time and is exposed to a phosphorus compound-containing exhaust gas, and an exhaust gas using the same. The present invention relates to a method for purifying (particularly, a phosphorus compound-containing exhaust gas).

  The present invention relates to a catalyst in which a decrease in catalytic performance is suppressed even when a large amount of a phosphorus compound adheres to the catalyst.

  Although a catalyst for purifying automobile exhaust gas has been developed in the past, further improvement in the ability to purify exhaust gas is required as regulations on automobile exhaust gas are tightened. In particular, there is a need for a catalyst that can achieve high exhaust gas purification performance under various engine use conditions.

  For example, the maintenance of exhaust gas purification performance for a long period of time has been required for automobile exhaust gas purification devices. This means that there is an increasing demand for longer catalyst life for purifying exhaust gas. In order to improve the long-term durability of the catalyst, suppression of sintering of the noble metal particles supported on the catalyst and suppression of sulfur poisoning have been studied. On the other hand, it is known that poisoning by phosphorus contained in exhaust gas (described as “phosphorus poisoning” in this specification) has a large effect on catalyst performance deterioration (Non-Patent Document 1). In order to satisfy regulations which will be further strengthened in the future, it is important to suppress the phosphorus poisoning or to improve the catalyst performance after the poisoning. In recent years, it has been required not only to suppress the poisoning of phosphorus but also to suppress the deterioration of the catalytic performance due to the poisoning even when exposed to high-temperature exhaust gas of 950 ° C. or more. The demand for longer life of the catalyst performance has been stricter than in the past, such as a demand for a reduction and a reduction in the catalyst performance due to phosphorus poisoning.

  It is known that a phosphorus compound derived from a lubricating oil additive such as zinc dialkyldithiophosphate is contained in exhaust gas as a substance causing phosphorus poisoning. It is known that when exhaust gas flows through a purification device, a phosphorus compound contained in the exhaust gas accumulates in and permeates the catalyst layer, thereby causing phosphorus poisoning and degrading the catalytic performance (non-catalytic performance). Patent Document 1).

  It is known that the decrease in catalyst performance due to phosphorus poisoning is due to the following phenomena. Phosphorus compounds deposited and infiltrated in the catalyst layer cause diffusion inhibition of exhaust gas in the catalyst layer. Further, cerium oxide, which is an oxygen storage / release material (also referred to as an oxygen storage material), which is often used in a three-way catalyst, reacts with a phosphorus compound to form cerium phosphate. When cerium phosphate is formed, oxygen storage and release do not occur. Therefore, when the atmosphere of the exhaust gas fluctuates lean or rich, the effect of alleviating the lean or rich state due to oxygen storage and release is not exhibited. The occurrence of such diffusion inhibition and oxygen storage / release inhibition phenomena lowers the exhaust gas purification rate.

  Patent Document 1 discloses that a composite oxide of ceria and zirconia is used in a catalyst using palladium to suppress phosphorus poisoning.

  Patent Literature 1 describes a catalyst using palladium whose performance is apt to be deteriorated due to phosphorus poisoning, and pays attention to the fact that ceria easily forms cerium phosphate. Patent Literature 1 discloses that by replacing ceria with a composite oxide of ceria and zirconia, a decrease in catalyst performance due to phosphorus poisoning is suppressed as compared with the related art. Patent Literature 1 does not discuss reduction in catalytic performance due to phosphorus poisoning of a catalyst using rhodium, which is the most active as a three-way catalyst.

  Further, Patent Literature 2 discloses that a region where a catalyst material is not applied is provided as a phosphorus capture region at an upstream end portion of a catalyst, thereby suppressing performance degradation due to phosphorus.

  Since a large amount of the phosphorus compound adheres to the upstream side in the exhaust gas flow direction, the catalyst described in Patent Literature 2 has a phosphorus capturing region containing no noble metal at the upstream end. However, Patent Literature 2 does not describe the catalytic performance after phosphorus poisoning, and its effect is unknown. Further, when the length of the catalyst from the upstream end to the downstream end is relatively short, it is considered that the phosphorus compound adheres to the vicinity of the downstream end of the catalyst to deteriorate the performance, and the long-term durability is reduced. It is hard to say that it is enough.

  Patent Literature 3 discloses a catalyst in which a single layer of only a palladium-supporting layer is disposed at an upstream end of a lower catalyst layer, and an upper catalyst layer is stacked on a downstream side to support rhodium.

  Patent Document 3 discloses that providing a single layer of palladium on the upstream side of the catalyst makes it easier for exhaust gas to diffuse to the lower catalyst layer, but Patent Document 3 discusses phosphorus poisoning. Absent. The performance of the catalyst described in Patent Document 3 under the condition that the exhaust gas contains a phosphorus compound is unknown.

  In Patent Document 4, a lower catalyst layer is provided on the entire substrate from the upstream end to the downstream end, and the upper catalyst layer is laminated on the upstream and downstream sides of the lower catalyst layer. There is disclosed a catalyst in which the surface of a lower catalyst layer is exposed without laminating an upper catalyst layer at an intermediate portion between an upstream side and a downstream side. However, in Patent Document 4, there are no specific values for the total length of the catalyst and the intermediate layer, and for the purpose of reducing the heat capacity of the catalyst, reducing the resistance to gas flow, and reducing the catalyst components, the phosphorus content in the exhaust gas is reduced. There is no description that the catalyst poisoning by the catalyst can be improved in relation to the entire length of the catalyst and the intermediate portion.

JP-A-8-38898 Japanese Patent Publication No. 2009-501079 Japanese Patent No. 4751917 Japanese Patent No. 4350250

A Scott et al. , SAE Paper, 96189 8, (1996).

  However, in conventional catalysts, there is still a need for further improvement in the ability to purify exhaust gas.

  For example, the catalysts disclosed in Patent Literatures 1 to 4 do not have sufficient ability to purify exhaust gas, and particularly have low catalytic performance after long-time phosphorus poisoning.

  The inventors of the present invention have made intensive studies and as a result, in an exhaust gas purification catalyst having an upstream first catalyst layer, a downstream second catalyst layer, and a third catalyst layer, an upstream portion of the third catalyst layer. The present inventors have found that the presence of an intermediate portion between the first and second catalyst layers between the first catalyst layer and the second catalyst layer improves the exhaust gas purification ability, and completed the present invention.

  According to a preferred embodiment of the present invention, for example, the following catalyst and the like are provided.

(Claim 1)
A catalyst for purifying exhaust gas, comprising a carrier, a first catalyst layer on an upstream side, a second catalyst layer on a downstream side, and a third catalyst layer,
An upstream portion of the third catalyst layer is on the first catalyst layer;
A downstream portion of the third catalyst layer is on the second catalyst layer;
An intermediate portion of the third catalyst layer between the upstream portion and the downstream portion exists between the first catalyst layer and the second catalyst layer;
Exhaust gas purification catalyst.

(Claim 2)
The thickness H ₄ of the intermediate portion is characterized thinner than the thickness H ₅ having a thickness of H ₃ and the downstream portion of the upstream portion catalyst according to 1.

(Claim 3)
Item 3. The catalyst according to item 1 or 2, wherein the ratio of the length of the first catalyst layer to the total length of the catalyst is 10% to 70%.

(Claim 4)
The catalyst according to any one of Items 1 to 3, wherein a ratio of a length of the intermediate portion of the third catalyst layer to a total length of the catalyst is 1% to 25%.

(Claim 5)
The first catalyst layer, the second catalyst layer, and the third catalyst layer all contain a noble metal, and the mass of the noble metal contained in the first catalyst layer is larger than the mass of the noble metal contained in the second catalyst layer. The catalyst according to any one of claims 1 to 4, wherein the amount is large.

(Claim 6)
The catalyst according to any one of Items 1 to 5, wherein the third catalyst layer contains rhodium and palladium, and the first catalyst layer and the second catalyst layer contain palladium.

(Claim 7)
7. The catalyst according to any one of items 1 to 6, wherein the first catalyst layer, the second catalyst layer, and the third catalyst layer contain cerium.

(Claim 8)
Item 8. The catalyst according to any one of Items 1 to 7, which is used for purifying exhaust gas from an engine containing a phosphorus compound.

(Claim 9)
Item 9. A method for purifying exhaust gas, comprising a step of bringing exhaust gas into contact with the catalyst according to any one of Items 1 to 8 above.

  In the present invention, it is contemplated that one or more of the features described above may be provided in addition to the explicitly specified combinations. Still further embodiments and advantages of the invention will be apparent to those skilled in the art upon reading and understanding the following detailed description, as appropriate.

  The catalyst of the present invention can exhibit an improved exhaust gas purifying effect. The catalyst according to the invention has, in particular, improved durability performance. The catalyst of the present invention can exhibit high catalytic performance even after being exposed to high temperatures. The catalyst of the present invention can exhibit high catalytic performance even at a high temperature and after prolonged exposure to an exhaust gas containing a phosphorus compound.

FIG. 1a is a schematic sectional view of one example of the exhaust gas purifying catalyst of the present invention. FIG. 1b is a schematic cross-sectional view illustrating the length and thickness of a catalyst layer of an example of the exhaust gas purifying catalyst of the present invention. FIG. 2 is a graph in which the ratio [%] of the length of the first catalyst layer to the total length of the catalyst is plotted on the horizontal axis, and the time to reach T50 [seconds] is plotted on the vertical axis. In FIG. 3, for the catalysts D, F, G, H and I, the ratio [%] of the length of the intermediate portion to the length of the entire catalyst is plotted on the horizontal axis, and the time to reach T50 [seconds] is plotted on the vertical axis. It is a graph. FIG. 4 shows the ratio [%] of the amount of noble metal in the first catalyst layer to the total amount of noble metal in the first catalyst layer and the second catalyst layer for catalysts C, J, K, L, and M. It is a graph in which the vertical axis indicates the time to reach [sec]. FIG. 5 is a graph in which the vertical axis represents the time [seconds] to reach T50 for catalysts C and N.

(Description of a preferred embodiment)
Hereinafter, preferred embodiments of the present invention will be described.

  The embodiments provided below are provided for a better understanding of the present invention, and it is understood that the scope of the present invention should not be limited to the following description. Therefore, it is apparent that those skilled in the art can appropriately make modifications within the scope of the present invention in view of the description in this specification. It is also understood that the following embodiments of the present invention can be used alone or in combination.

  It should be noted that the singular and plural forms do not basically exist in Japanese, and therefore, throughout this specification, the term singular and plural terms includes both the singular and plural forms unless specifically stated otherwise. It is understood that. Therefore, when a foreign language specification is prepared based on this specification, even if the singular form is used in the foreign language specification, it is intended in the original Japanese language unless otherwise specified. It should be understood to include both singular and plural concepts. Therefore, it is understood that terms in the foreign language in which singular articles (eg, "a", "an", etc. in English) are used also include the concept of the plural unless otherwise specified. Should. It should also be understood that the terms used in this specification are used in a meaning commonly used in the art unless otherwise specified. Thus, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. However, when a definition of a term is described in this specification, the term is interpreted based on the definition.

(Definition of terms)
The terms used in this specification are described below.

  As used herein, the term "catalyst layer" refers to a material formed on a carrier with a refractory inorganic oxide and a catalyst component, or a material containing the catalyst component further formed on the catalyst layer. It refers to what has been formed. In the present invention, there are "catalyst layers" such as a first catalyst layer, a second catalyst layer, and a third catalyst layer.

  In the present specification, the “carrier” refers to, for example, a refractory three-dimensional structure that supports a catalyst component and the like. Specifically, it is a monolithic carrier, such as a monolith honeycomb carrier. A catalyst layer can be formed on the support.

  “Per liter of carrier” means “per liter of bulk volume of the carrier including the volume of voids formed inside the carrier”. The mass of each component per liter of carrier can be expressed as g / L. The catalyst should be manufactured so that the catalyst layer is not formed on the outer surface of the carrier through which the exhaust gas is difficult to flow, and even if the catalyst layer is formed on the outer surface of the carrier, the thickness of the catalyst layer is determined by the size of the carrier. Taking into account that it is about three orders of magnitude smaller, the volume of the support and the volume of the catalyst are comparable. Therefore, "per liter of carrier" and "1 liter of catalyst volume" can be treated equally.

  In the present specification, “upstream” refers to a portion near the side where exhaust gas flows into the catalyst, and “downstream” refers to a portion near the side where exhaust gas is discharged from the catalyst.

  In this specification, the phrase “the B layer is“ laminated ”on the A layer” means that the B layer exists on the A layer, and at this time, one or a plurality of layers are provided between the A layer and the B layer. Layers may be present. In the “laminated” state, a layer may be present on the carrier.

Further, “the B layer is directly laminated on the A layer” means that the upper surface of the A layer is in contact with the bottom surface of the B layer. For example, in the catalyst shown in FIG. 1a, the upstream part (D ₁ ) of the third catalyst layer is directly laminated on the first catalyst layer (B), and the downstream part (D ₃ ) of the _third catalyst layer is formed on the second catalyst layer. (C) is directly laminated. In the “directly laminated” state, the layers may be directly laminated on the carrier.

  In this specification, for each catalyst layer, the “length of the catalyst layer” refers to the distance in the exhaust gas flow direction in the region where the catalyst layer is stacked on the carrier.

  In this specification, for each catalyst layer, the “thickness of the catalyst layer” refers to a distance in a direction perpendicular to the exhaust gas flow direction in a region where the catalyst layer is stacked on the carrier.

  In the present specification, the “phosphorus compound” refers to a compound containing a phosphorus element.

  In the present specification, "phosphorus poisoning" refers to a phenomenon in which the purification ability of a catalyst is reduced by contact of a phosphorus compound contained in exhaust gas with the catalyst.

  In this specification, "per liter of catalyst volume" means "per liter of bulk volume of the catalyst including the volume of voids formed inside the catalyst". The mass of each component per liter of catalyst volume can be expressed as g / L.

  In the present specification, when a range is described by the expression “A to B”, the range means “A or more and B or less”. That is, the range includes the upper limit and the lower limit.

(Exhaust gas purification catalyst)
The catalyst of the present invention is a catalyst for purifying exhaust gas, and has a carrier, an upstream first catalyst layer, a downstream second catalyst layer, and a third catalyst layer.

  The "first catalyst layer" is a layer that is directly laminated on a carrier in a catalyst or a layer laminated on a layer in which one or more layers are laminated on a carrier, and refers to a layer laminated on an upstream side, The “second catalyst layer” refers to a layer that is laminated directly on a carrier or a layer in which one or more layers are laminated on a carrier in a catalyst, and is a layer that is laminated on a downstream side. The first catalyst layer exists on the upstream side of the second catalyst layer with the intermediate portion interposed therebetween.

  The “third catalyst layer” refers to a layer of the catalyst that is stacked above the first catalyst layer and the second catalyst layer. The third catalyst layer has an upstream portion, a downstream portion, and an intermediate portion between the upstream portion and the downstream portion, and the upstream portion of the third catalyst layer is located above the first catalyst layer. And a downstream portion of the third catalyst layer is present on the second catalyst layer, and an intermediate portion between the upstream portion and the downstream portion of the third catalyst layer is provided between the first catalyst layer and the third catalyst layer. Exists between the two catalyst layers.

  Between the first catalyst layer and the second catalyst layer, not only the intermediate part of the third catalyst layer exists directly on the carrier, but also one or more layers between the third catalyst layer and the carrier. May be present. Here, one or more layers may exist between the third catalyst layer and the first catalyst layer. One or more layers may be present between the third catalyst layer and the second catalyst layer. Also, one or more layers may be present between the first catalyst layer and the carrier. One or more layers may also be present between the second catalyst layer and the support.

  Hereinafter, the configuration of the exhaust gas purifying catalyst according to one embodiment of the present invention will be described with reference to FIG. 1A. Note that FIG. 1A is a diagram schematically illustrating a positional relationship between the catalyst layers, and does not represent an actual distance or shape.

Although the configuration of the catalyst of the present invention is not limited to this, for example, as shown in FIG. 1A, a carrier (A), an upstream first catalyst layer (B), and a downstream second catalyst layer (C) and a third catalyst layer (D: the third catalyst layer (D) includes an upstream portion (D ₁ ), an intermediate portion (D ₂ ), and a downstream portion (D ₃ )). The upstream portion (D ₁ ) of the third catalyst layer is present on the first catalyst layer (B), and the downstream portion (D ₃ ) of the third catalyst layer is provided on the second catalyst layer (C). An intermediate portion (D ₂ ) between the upstream portion (D ₁ ) and the downstream portion (D ₃ ) of the _third catalyst layer is present on the first catalyst layer (B) and the second catalyst layer ( C). In Figure 1b, L total length of the catalyst, L ₁ is a first catalyst layer (third upstream portion of the catalyst layer) of the length, L ₂ is the middle part length, L ₃ is a second catalyst layer (3 (A downstream portion of the catalyst layer).

(Length of catalyst layer)
The first catalyst layer is provided from the inflow side end face to the outflow side, and the length of the first catalyst layer corresponds to the position where the intermediate portion starts, as shown in FIG. 1a. That is, the ratio of the length of the first catalyst layer to the entire length of the catalyst (L ₁ / L × 100) also indicates the start position of the intermediate portion relative to the entire length of the catalyst, and is preferably 10% or more, and more preferably 15% or more. Or more, and most preferably 25% or more. The ratio (L ₁ / L × 100) is preferably 70% or less, more preferably 60% or less, and most preferably 48% or less. If the length of the first catalyst layer is too short, the space velocity with respect to the total volume of the first catalyst layer increases, and the time during which the exhaust gas contacts the first catalyst layer is shortened. Not preferred. If the length of the first catalyst layer is too long, the starting position of the intermediate portion is closer to the downstream side, so that a desired ratio of the phosphorus compound is less likely to be deposited on the intermediate portion, so that the performance is likely to deteriorate due to phosphorus poisoning, which is not preferable.

  Here, the length of each catalyst layer is an average of the value Lmin at which the length of the catalyst layer is the shortest and the value Lmax at which the length is the longest ((Lmin + Lmax) ÷ 2).

The ratio of the length of the intermediate portion to the total length of the catalyst (L ₂ / L × 100) is preferably at least 1%, more preferably at least 4%, and most preferably at least 7%, based on the total length of the catalyst. . The ratio of the length of the intermediate portion to the total length of the catalyst (L ₂ / L × 100) is preferably 25% or less, more preferably 18% or less, and most preferably 12% or less, based on the total catalyst length. . If the ratio of the length of the intermediate portion to the total length of the catalyst is too small, it is not preferable because the phosphorus compound cannot be sufficiently deposited, and if it is too large, the first catalyst layer becomes too short, which is not preferable. Further, the length of the second catalyst layer is too short, which is not preferable.

The ratio of the length of the second catalyst layer to the total catalyst length (L ₃ / L × 100) is preferably at least 35%, more preferably at least 50%, and most preferably at least 55%. The ratio of the length of the second catalyst layer to the total catalyst length (L ₃ / L × 100) is preferably 95% or less, more preferably 90% or less, and most preferably 80% or less. The second catalyst layer is provided from the outflow side end face toward the inflow side. If the length of the second catalyst layer is too short, the intermediate portion is close to the outflow side, and a desired proportion of the phosphorus compound is difficult to deposit on the intermediate portion, so that the performance is likely to deteriorate due to phosphorus poisoning, which is not preferable. If the length of the second catalyst layer is too long, the second catalyst layer becomes susceptible to phosphorus poisoning, which is not preferable.

  In one preferred embodiment, the sum of the length of the first catalyst layer, the length of the second catalyst layer and the length of the middle part is equal to the length of the support. Also, in one preferred embodiment, the length of the third catalyst layer is equal to the length of the support. In a more preferred embodiment, the sum of the length of the first catalyst layer, the length of the second catalyst layer and the length of the intermediate portion is equal to the length of the carrier, and the length of the third catalyst layer is equal to the length of the carrier. Is equal to Further, the length of the second catalyst layer is preferably at least 0.5 times, more preferably at least 1.0 times, most preferably at least 1.8 times the length of the first catalyst layer. That is all. The length of the second catalyst layer is preferably 5 times or less, more preferably 4 times or less, and most preferably 3 times or less with respect to the length of the first catalyst layer.

(Thickness of catalyst layer)
The thicknesses of the first catalyst layer, the second catalyst layer, and the third catalyst layer are not particularly limited. It can be appropriately designed so that the exhaust gas purifying ability can be appropriately exhibited. If the thickness of each catalyst layer is too large, it is not preferable because the exhaust pressure increases, and if it is too small, it is not preferable because sufficient purification efficiency cannot be obtained.

Total H ₃ of a thickness of the upstream portion D ₁ of the thickness of the third catalyst layer of the first catalyst layer B is preferably higher than the thickness H ₄ of the intermediate portion of the third catalyst layer. H ₄ is preferably at least 40% of H ₃ . H ₄ is preferably at most 95%, more preferably at most 80%, most preferably at most 70% of H ₃ .

Total H ₅ of the thickness of the downstream portion D ₃ of the thickness and the third catalyst layer of the second catalyst layer C is preferably higher than the thickness H ₄ of the intermediate portion of the third catalyst layer. H ₄ is preferably at least 40% of H ₅ . H ₄ is preferably at most 95%, more preferably at most 80%, most preferably at most 70% of H ₅ .

Total H ₅ of the thickness of the downstream portion D ₃ of the thickness and the third catalyst layer of the second catalyst layer C, the total thickness and the thickness of the upstream portion D ₁ of the third catalyst layer of the first catalyst layer B It is preferably at least 40% with respect to H ₃ . The total H ₅ of the thickness of the downstream portion D ₃ of the thickness and the third catalyst layer of the second catalyst layer, the total thickness of the upstream portion thickness D ₁ of the third catalyst layer of the first catalyst layer H ₃ Is preferably 100% or less, more preferably 95% or less, and most preferably 90% or less.

  The thickness of each catalyst layer is an average value ((Hmin + Hmax) ÷ 2) of a value Hmin at which the thickness of the catalyst layer becomes the smallest and a value Hmax at which the thickness becomes the largest. The thickness of each catalyst layer need not be uniform over its entirety, but is preferably substantially uniform over substantially the entirety.

(Carrier)
As the carrier, a carrier known as a carrier of an exhaust gas purifying catalyst can be used. The shape of the carrier is preferably a three-dimensional shape that enables efficient contact between the exhaust gas and the catalyst layer. For example, a honeycomb shape can be preferably used. Further, an integrally molded carrier (integral structure) can be preferably used. For example, a monolith honeycomb carrier, a metal honeycomb carrier, a plugged honeycomb carrier such as a diesel particulate filter, a punching metal, or the like is preferably used.

As the monolith honeycomb carrier, one usually called a ceramic honeycomb carrier is suitably used. In particular, a honeycomb carrier made of cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, aluminum titanate, betalite, sponge, aluminosilicate, magnesium silicate, or the like is preferable. Particularly preferred. In addition, an integrated structure using an oxidation-resistant heat-resistant metal such as stainless steel or an Fe—Cr—Al alloy is used. These monolithic carriers are manufactured by, for example, an extrusion molding method or a method of winding a sheet-shaped element. As the shape (cell shape) of the gas passage, any known shape can be used. For example, hexagons, squares, triangles, or corrugations can be used. The cell density (number of cells / unit cross-sectional area) is preferably at least 100 cells / square inch (6.45 cm ² ), and more preferably at least 200 cells / square inch (6.45 cm ² ). Further, it is preferably at most 600 cells / square inch (6.45 cm ² ), and more preferably at most 500 cells / square inch (6.45 cm ² ).

  The length of the carrier can be appropriately designed, and is preferably 10 mm or more, more preferably 15 mm or more, and further preferably 30 mm or more. The length of the carrier is preferably 1000 mm or less, more preferably 300 mm or less, and even more preferably 200 mm or less. When the length of the support is too short, it is difficult to perform sufficient purification, and when the length is too long, the mass of the catalyst becomes heavy.

(Material of catalyst layer)
The first catalyst layer, the second catalyst layer, and the third catalyst layer each include a catalyst component. Preferred catalyst components include noble metals, oxygen storage materials, oxides of Group 2 elements, oxides of Group 1 elements, and refractory inorganic oxides (oxygen storage materials, oxides of Group 2 elements, or Group 1 element oxides). Element compounds (excluding oxides), Group 2 element compounds (excluding oxides), Group 1 element compounds (excluding oxides), rare earth metal compounds (excluding oxygen storage materials), and the like.

For example, specific examples of the noble metal include platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), and the like. It is preferable to use Pt, Pd, or Rh. One of these noble metals may be used alone, or two or more thereof may be used in combination. Without being bound by theory, palladium can efficiently purify hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas, and rhodium can efficiently purify nitrogen oxides (NO _x ). Because you can. In addition to rhodium and palladium, other precious metal elements (for example, gold, silver, platinum, ruthenium, osmium, or iridium) may be further included, but not limited thereto.

  The noble metal contained in the first catalyst layer is preferably rhodium and / or palladium, more preferably palladium. One of these noble metals may be used alone, or two may be used in combination. The noble metal contained in the second catalyst layer is preferably rhodium and / or palladium, more preferably palladium. One of these noble metals may be used alone, or two may be used in combination. The noble metal contained in the third catalyst layer is preferably rhodium and / or palladium and / or platinum, more preferably rhodium and / or palladium. One of these noble metals may be used alone, two may be used in combination, or three may be used in combination.

  When a noble metal is used, the amount of the noble metal used in the catalyst layer (the amount supported) is not particularly limited and can be appropriately selected according to the specifications of the engine to be used. If a sufficient amount of noble metal is present, exhaust gas can be purified with high efficiency.

  When the noble metal is palladium, the amount of the noble metal in the first catalyst layer is preferably 0.05 g or more, more preferably 0.07 g or more, and more preferably 0.1 g or more per liter of the catalyst volume. Is more preferable. When the noble metal is palladium, the amount of the noble metal in the first catalyst layer is preferably 15 g or less, more preferably 10 g or less, and still more preferably 5 g or less per liter of the catalyst volume. . If the amount of the noble metal is too large, the cost of the catalyst increases. When the noble metal is rhodium, the amount of the noble metal in the first catalyst layer is preferably 0.01 g or more, more preferably 0.05 g or more, and more preferably 0.1 g or more per liter of the catalyst volume. Is more preferable. When the noble metal is rhodium, the amount of the noble metal in the first catalyst layer is preferably 10 g or less, more preferably 8 g or less, and even more preferably 5 g or less per liter of catalyst volume. If the amount of the noble metal is too large, the cost of the catalyst increases. If the amount of the noble metal is too small, sufficient exhaust gas purification performance cannot be exhibited after thermal deterioration or after poisoning with phosphorus, which is not preferable.

  The ratio between the amount of the noble metal contained in the first catalyst layer and the mass of the noble metal contained in the second catalyst layer is determined by the sum of the mass of the noble metal contained in the first catalyst layer and the mass of the noble metal contained in the second catalyst layer. As 100%, the mass of the noble metal contained in the first catalyst layer is preferably 20% or more, more preferably 30% or more, further preferably 40% or more, and more preferably 50% or more. Is particularly preferred, and particularly preferably 60% or more. In addition, the mass of the noble metal element contained in the first catalyst layer is preferably 100% or less, more preferably 86% or less, further preferably 80% or less, and more preferably 74% or less. It is remarkably preferable, and particularly preferably 70% or less.

  The ratio of the mass of the noble metal contained in the third catalyst layer to the total mass of the noble metal contained in the first catalyst layer and the second catalyst layer is determined by the ratio of the mass of the noble metal contained in the first catalyst layer to that contained in the second catalyst layer. Assuming that the total mass of the noble metal is 100%, the mass of the noble metal contained in the third catalyst layer is preferably 0% or more, more preferably 5% or more, even more preferably 8% or more. And 10% or more. Further, the mass of the noble metal contained in the third catalyst layer is preferably 150% or less, more preferably 100% or less, further preferably 80% or less, and particularly preferably 60% or less. , And particularly preferably 40% or less.

  In the present invention, when rhodium and palladium are contained in the third catalyst layer, the relative ratio (Pd / Rh) of the amount of palladium to the amount of rhodium is not particularly limited, and is preferably 0.1 times or more. Yes, more preferably 0.3 times or more, even more preferably 0.6 times or more. When rhodium and palladium are contained in the third catalyst layer, the relative ratio of the amount of palladium to the amount of rhodium (Pd / Rh) is not particularly limited, and is preferably 5 times or less, more preferably 2 times or less. And more preferably 1.35 times or less. If the Pd / Rh ratio is too low, the air-warming property is not good.

  The compound of the noble metal element used in the above-mentioned preparation method is not particularly limited, and for example, palladium, or rhodium and palladium may be added as it is, or may be added in another form, and then the desired It may be converted to a form (Pd, or a form of Rh and Pd). In a preferred embodiment of the invention, it is preferred to add the compound of rhodium or the compound of rhodium and palladium to the aqueous medium, in which embodiment the rhodium or rhodium and palladium are in other forms, especially water-soluble. It is preferably added in the form of a noble metal salt. Hereinafter, the compound of the noble metal element is also referred to as “water-soluble noble metal salt”. Here, usable water-soluble noble metal salts are not particularly limited. Various raw materials for the noble metal catalyst component used in the field of exhaust gas purification can be used. Specifically, for example, in the case of rhodium, for example, rhodium; halides such as rhodium bromide and rhodium chloride; dinitrodiammine salts, hexaammine salts, hexahydroxo acid salts, tetraammine salts, and tetranitro acid salts of rhodium. Inorganic salts; carboxylate salts such as acetate salts; and hydroxides, alkoxides, oxides and the like. Preferably, a dinitrodiammine salt, a hexaammine salt, a hexahydroxo acid salt and a tetraammine salt are mentioned, and a dinitrodiammine salt (dinitrodiamminerhodium) and a tetraammine salt are more preferable. In the case of palladium, halides such as palladium; palladium chloride; inorganic salts of palladium such as nitrates, sulfates, dinitrodiammines, hexaammines, tetraammines, and hexacyanoates; carboxyls such as acetates Acid salts; and hydroxides, alkoxides, oxides and the like. Preferably, nitrates, hexaammine salts and tetraammine salts are mentioned, and nitrates (palladium nitrate) and tetraammine salts are more preferred. In the present invention, each of the rhodium and palladium compounds (rhodium and palladium sources) may be a single compound or a mixture of two or more compounds.

  The state of the catalyst component in the catalyst layer is not particularly limited. For example, in the catalyst layer formed on the support surface, the catalyst component may be in a form dispersed alone, or may be supported in the refractory inorganic oxide described below is dispersed in the catalyst layer. Good. Among these, a form in which the catalytically active component is carried on the surface of an oxygen storage material described later is preferable. By supporting the noble metal on the oxygen storage material, the oxygen stored and released in the oxygen storage material can be efficiently used for the oxidation and reduction reactions catalyzed by these noble metals.

  Preferred examples of the oxygen storage material include cerium oxide, oxides composed of cerium and other elements, such as cerium-zirconium composite oxide, cerium-zirconium-lanthanum composite oxide, and cerium-zirconium-lanthanum-neodymium composite. Oxide, cerium-zirconium-lanthanum-yttrium composite oxide, and the like. Further, the crystal structure of the oxygen storage material, cubic, tetragonal, monoclinic, orthorhombic, etc., preferably cubic, tetragonal, monoclinic, more preferably cubic, tetragonal It is.

A cerium raw material such as a cerium-zirconium composite oxide used as an oxygen storage material is not particularly limited, and a raw material used in the field of exhaust gas purification can be used. Specific examples include nitrates such as cerous nitrate, carbonates and sulfates. Of these, nitrates are preferably used. In the present invention, the cerium source may be a single substance or a mixture of two or more kinds. Here, the addition amount of the cerium source is preferably 1 g or more, more preferably 3 g or more, and still more preferably 5 g or more per liter of a carrier (for example, a refractory three-dimensional structure) in terms of cerium oxide (CeO ₂ ). . The amount of the cerium source added is preferably 200 g or less, more preferably 100 g or less, and still more preferably 50 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of cerium oxide (CeO ₂ ).

The zirconium raw material is not particularly limited, and a raw material used in the field of exhaust gas purification can be used. Specific examples include zirconium oxynitrate, zirconium oxychloride, zirconium nitrate, and basic zirconium sulfate. Of these, zirconium oxynitrate and zirconium nitrate are preferably used. In the present invention, the zirconium source may be a single substance or a mixture of two or more kinds. Here, the addition amount of the zirconium source is preferably 5 g or more, more preferably 10 g or more, and still more preferably 20 g or more per liter of a carrier (for example, a refractory three-dimensional structure) in terms of zirconium oxide (ZrO ₂ ). . The amount of the zirconium source to be added is preferably 200 g or less, more preferably 150 g or less, more preferably 100 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of zirconium oxide (ZrO ₂ ).

The lanthanum raw material is not particularly limited, and a raw material used in the field of exhaust gas purification can be used. Specific examples include lanthanum hydroxide, lanthanum nitrate, lanthanum acetate, lanthanum oxide, and the like. Of these, lanthanum nitrate or lanthanum hydroxide is preferred. The lanthanum source may be a single substance or a mixture of two or more. Here, the addition amount of the lanthanum source may be 0 g per liter of a carrier (for example, a refractory three-dimensional structure) in terms of lanthanum oxide (La ₂ O ₃ ), but is preferably 0.1 g or more. It is more preferably 0.5 g or more, and further preferably 1 g or more. The amount of the lanthanum source to be added is preferably 50 g or less, more preferably 35 g or less, and still more preferably 20 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of lanthanum oxide (La ₂ O ₃ ).

The yttria raw material is not particularly limited, and a raw material used in the field of exhaust gas purification can be used. Specific examples include yttrium hydroxide, yttrium nitrate, yttrium oxalate, yttrium sulfate and the like. Among these, yttrium hydroxide and yttrium nitrate are preferably used. In the present invention, the yttrium source may be a single substance or a mixture of two or more kinds. Here, the addition amount of the yttrium source may be 0 g per liter of a carrier (for example, a refractory three-dimensional structure) in terms of yttrium oxide (Y ₂ O ₃ ), but is preferably 0.1 g or more. 0.5 g or more is more preferable, and 1 g or more is more preferable. The amount of the yttrium source to be added is preferably 50 g or less, more preferably 35 g or less, more preferably 20 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of yttrium oxide (Y ₂ O ₃ ). is there.

The neodymium raw material is not particularly limited, and a raw material used in the field of exhaust gas purification can be used. Specific examples include neodymium hydroxide, neodymium nitrate, neodymium oxalate, neodymium sulfate, and the like. Of these, neodymium hydroxide and neodymium nitrate are preferably used. In the present invention, the neodymium source may be a single substance or a mixture of two or more. Here, the addition amount of the neodymium source may be 0 g per liter of a carrier (for example, a refractory three-dimensional structure) in terms of neodymium oxide (Nd ₂ O ₅ ), but is preferably 0.1 g or more, 0.5 g or more is more preferable, and 1 g or more is more preferable. The addition amount of the neodymium source is preferably 50 g or less, more preferably 35 g or less, and still more preferably 20 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of neodymium oxide (Nd ₂ O ₅ ).

  The shape of the oxygen storage material is not particularly limited. Preferred shapes of the oxygen storage material include, for example, granules, fine particles, powders, cylinders, cones, prisms, cubes, pyramids, and irregular shapes. More preferably, the shape of the oxygen storage material is granular, fine particle, or powder. The average particle size of the oxygen storage material when the shape is granular, fine particle, or powdery is not particularly limited, but is, for example, preferably 1.0 μm or more, and more preferably 5.0 μm or more. . Further, it is preferably 100 μm or less, more preferably 20.0 μm or less. The “average particle size” of the oxygen storage material can be measured by a known method such as classification.

The oxygen storage material preferably has an appropriate BET specific surface area. Having an appropriate BET specific surface area increases the ability to store and release oxygen in the exhaust gas. The BET specific surface area of the oxygen storage material is preferably at least 10 m ² / g, more preferably at least 50 m ² / g. Further, it is preferably at most 300 m ² / g, more preferably at most 200 m ² / g.

  The method for producing the oxygen storage material is not particularly limited. It is possible to use products manufactured by various known manufacturing methods.

Each of the first catalyst layer, the second catalyst layer, and the third catalyst layer may include a Group 1 element, a Group 2 element, a rare earth metal element, and other transition metal elements as necessary. Examples of the Group 1 element and the Group 2 element include potassium, magnesium, calcium, strontium, barium and the like. These may be used alone or in the form of a mixture of two or more. be able to. The Group 1 element or Group 2 element used in the present invention can be used in the form of an oxide, a sulfate, a carbonate, a nitrate, or the like, and is preferably an oxide, a sulfate, or a carbonate. BaSO ₄ can be used as the barium sulfate. The amount of barium sulfate may be 0 g per liter of a carrier (for example, a refractory three-dimensional structure) in terms of BaSO ₄ , but is preferably 0.1 g or more, more preferably 0.3 g or more, and Preferably, it is 0.5 g or more. The amount of barium sulfate is preferably 50 g or less, more preferably 30 g or less, further preferably 20 g or less per liter of a carrier (for example, a refractory three-dimensional structure) in terms of BaSO ₄ .

(Refractory inorganic oxide)
The catalyst layer used in the exhaust gas purifying catalyst of the present invention preferably contains a refractory inorganic oxide. The refractory inorganic oxide can be used as a catalyst-carrying material for carrying a catalytically active component such as the above-mentioned noble metals, rare earth metals, and other metal elements. As the refractory inorganic oxide, any inorganic oxide known as a material supporting a catalyst component for purifying exhaust gas can be used. Specifically, aluminum oxide (Al ₂ O ₃ ) such as α-alumina or activated alumina such as γ, δ, η, and θ; silicon oxide (SiO ₂ ); titanium oxide (titania) (TiO ₂ ); Zirconium oxide (ZrO ₂ ); phosphorus oxide (P ₂ O ₅ ); zeolite phosphate; or a composite oxide thereof, for example, alumina-titania, alumina-zirconia, titania-zirconia, and the like. Aluminum, silicon oxide (silica), phosphorus oxide, titanium oxide and zirconium oxide are preferred, silicon oxide (silica) and aluminum oxide are more preferred, and activated alumina powder is even more preferred. Here, as these refractory inorganic oxides, one kind of substance may be used alone, or a mixture of two or more kinds of substances may be used. These may be used in the form of an oxide as described above, or a precursor material capable of forming an oxide by heating may be used. Examples of precursor materials that can form oxides upon heating include the above aluminum, silicon, titanium, zirconium, phosphorus, hydroxides, nitrates, halides such as chlorides, acetates, sulfates, carbonates and the like. Is mentioned.

  The amount of the refractory inorganic oxide contained in the catalyst of the present invention is preferably at least 10 g, more preferably at least 50 g, per liter of the catalyst volume. Further, the weight is preferably 300 g or less, and more preferably 150 g or less. If a sufficient amount is used, it becomes possible to sufficiently disperse a catalyst component such as a noble metal, and it is possible to sufficiently ensure durability. On the other hand, when the amount is not too large, the catalyst component such as a noble metal and the exhaust gas can be brought into appropriate contact with each other, and as a result, the temperature is easily increased and the oxidation / reduction reaction can be suitably performed.

The BET specific surface area of the refractory inorganic oxide is preferably 50 m ² / g or more, and more preferably 150 m ² / g or more, from the viewpoint of supporting a catalytically active component such as a noble metal. Further, it is preferably 2000 m ² / g or less, and more preferably less 750m ² / g. The average particle diameter of the refractory inorganic oxide powder is preferably 0.5 μm or more, more preferably 1 μm or more. Further, the thickness is preferably 150 μm or less, and more preferably 100 μm or less.

The proportion of the refractory inorganic oxide is 1000 ° C. or higher 1100 ° C. after exposure to the waste gas for the previous BET specific surface area _{S 1} which is exposed to the following exhaust gas BET specific surface area _{S 2 (S 2 / S 1} × 100) is preferably at least 5%, more preferably at least 10%, even more preferably at least 30%. It is preferably at most 90%, more preferably at most 70%, even more preferably at most 60%.

(Production method of catalyst)
The catalyst of the present invention can be produced by applying a known catalyst production method.

  In the method for producing the catalyst of the present invention, it is preferable to use a slurry or an aqueous solution containing a compound (raw material) of a noble metal element (for example, Pd or Rh and Pd). Specifically, for example, first, a desired amount of a refractory inorganic oxide, an oxygen storage material, a compound (raw material) of a Group 2 element, and the like are mixed, and the mixture is mixed for an appropriate time (preferably, 15 minutes or more, and more preferably, After stirring for 24 hours or less), a compound (raw material) of a noble metal element (for example, Pd) is mixed with the slurry, and further stirred for an appropriate time (preferably 15 minutes or more, and more preferably 24 hours or less). . Next, the obtained slurry is put into a wet pulverizer, and pulverized for an appropriate time (preferably 15 minutes or more, and preferably 5 hours or less), so that the first catalyst layer, the second catalyst layer, and the third A slurry containing a raw material of a catalyst component to be laminated as a catalyst layer or the like is obtained. The amount of the solid substance in the slurry is preferably 5% by mass or more, more preferably 10% by mass or more with respect to the slurry. The amount of the solid matter in the slurry is preferably 60% by mass or less, more preferably 50% by mass or less with respect to the slurry. The wet pulverization method is generally performed by a known method, and is not particularly limited. For example, a method of performing wet pulverization using a ball mill or the like is possible.

  In addition, the aqueous solution of the compound (raw material) of the noble metal element (for example, Pd or Rh) means an aqueous solution containing the compound (raw material) of Pd when only palladium is used as the noble metal element. When rhodium and palladium are used in combination as a noble metal element, it means an aqueous solution containing a Rh compound (raw material) and a Pd compound (raw material). At this time, the aqueous solution is an aqueous solution of the Rh compound (raw material). It may be a mixed solution of an aqueous solution and an aqueous solution of a Pd compound (raw material), or may be a solution in which a Rh compound (raw material) and a Pd compound (raw material) are dissolved in the same solution.

  As a solvent for uniformly dissolving the above-mentioned water-soluble noble metal salt, water, alcohol and a mixture thereof can be used. As the alcohol, ethanol, 1-propanol, 2-propanol can be used. The concentration (content) of the water-soluble metal salt in the solvent is not particularly limited, and can be appropriately selected depending on the amount of the noble metal element supported.

  More specifically, for example, a slurry for laminating a catalyst component as a first catalyst layer, a second catalyst layer, and a third catalyst layer, respectively, is prepared, and the present invention is placed on a carrier (for example, a refractory three-dimensional structure). Each slurry is applied to a desired position so as to have a layer structure of a desired length, thickness and amount. For example, the first catalyst slurry is applied from the upstream end face toward the downstream side, dried, and then fired. Subsequently, the slurry for the second catalyst is applied from the downstream end face toward the upstream side, dried, and fired. Next, the slurry of the third catalyst is applied from the upstream end face to the downstream end face, dried, and calcined to obtain the catalyst of the present invention. Here, the order of applying the first catalyst layer slurry and the second catalyst slurry is not particularly limited. Further, the respective calcinations after applying and drying the slurry for the first catalyst layer and the slurry for the second catalyst layer are not necessarily required, and the third catalyst is applied after the slurry for the first catalyst layer and the slurry for the second catalyst layer are applied. After applying the layer slurry, baking may be performed. After the slurry for the third catalyst layer is applied, drying and baking may be performed separately, or may be performed as one step while increasing the furnace temperature.

  As a method of confirming the application state, length, and thickness of each slurry when preparing the above-mentioned catalyst, for example, the catalyst previously applied under some application conditions is destroyed, and the above-described length, thickness, and amount are used. Can be confirmed using a microscope such as a caliper, an electronic balance, and a three-dimensional (3D) microscope. Further, the length and the thickness can be measured without destroying the catalyst using an X-ray CT apparatus. A suitable catalyst can be easily produced by performing the coating under the conditions confirmed to be applied in a desired length, thickness and amount.

  After each of the slurries thus obtained is immersed in a three-dimensional structure so as to have a desired length, thickness and amount, the slurry is applied at an appropriate temperature (preferably 50 ° C. or higher, and preferably 300 ° C. or lower). After drying for an appropriate time (preferably 5 minutes or more, preferably 30 minutes or more, and preferably 10 hours or less, more preferably 8 hours or less), if necessary, an appropriate temperature (preferably 300 ° C. or more, Preferably, it is 400 ° C. or more, and preferably 1200 ° C. or less, more preferably 700 ° C. or less, for an appropriate time (preferably 10 minutes or more, more preferably 30 minutes or more, and preferably 10 hours or less. (More preferably 5 hours or less). Thus, a catalyst layer is formed on the carrier or the catalyst layer.

  The catalyst of the present invention is useful as a catalyst for an engine used for a long time. For example, in an engine used for 100 hours or more, or 1000 hours or more, the catalyst of the present invention can purify exhaust gas over a long period of time such as 100 hours or more, or 1000 hours or more.

  The internal combustion engine is not particularly limited. For example, a gasoline engine, a hybrid engine, an engine using natural gas, ethanol, dimethyl ether, or the like as a fuel can be used. Among them, a gasoline engine is preferable.

  The time for exposing the exhaust gas purifying catalyst to the exhaust gas is not particularly limited, and it is sufficient that at least a portion of the exhaust gas purifying catalyst is in contact with the exhaust gas.

  The temperature of the exhaust gas is not particularly limited, but is preferably, for example, 0 ° C. or higher, and more preferably 800 ° C. or lower. That is, the temperature is preferably within the temperature range of the exhaust gas during normal operation. Here, the air-fuel ratio (A / F; air / fuel) in the exhaust gas of the internal combustion engine having a temperature of 0 ° C. to 800 ° C. is preferably 10 or more, and more preferably 11 or more. The air-fuel ratio is preferably less than 30, more preferably 19 or less.

  The catalyst of the present invention as described above or the catalyst produced by the method as described above may be exposed to exhaust gas having a temperature higher than 800 ° C. For example, it may be exposed to an exhaust gas having a temperature of 800C to 1200C. Here, it is preferable that the air-fuel ratio of the exhaust gas having a temperature of 800 to 1200 ° C. is 10 to 18.6. The time for exposing the exhaust gas purifying catalyst to the exhaust gas having a temperature of 800 ° C to 1200 ° C is not particularly limited, and may be, for example, 5 to 500 hours. Even after exposure to such high-temperature exhaust gas, the catalyst of the present invention has high performance. In order to examine the exhaust gas purification performance of the catalyst after being exposed to such high-temperature exhaust gas, the catalyst was subjected to a treatment of exposing to 800 to 1200 ° C. exhaust gas for 5 to 500 hours as a heat treatment. It is effective to examine the exhaust gas purification performance.

Exhaust gas for which the present invention exhibits a particularly advantageous effect is an exhaust gas containing a phosphorus compound, and the catalyst of the present invention can purify the exhaust gas even when exposed to the phosphorus compound in the exhaust gas for a long time. it can. Even when the catalyst is exposed to the exhaust gas containing the phosphorus compound, the phosphorus compound accumulates per liter of a carrier (for example, a three-dimensional structure), for example, 1 g or more in terms of phosphorus oxide (P ₂ O ₅ ) in terms of phosphorus oxide (P ₂ O ₅ ). Since a considerable amount of the phosphorus compound is deposited on the upstream portion and the intermediate portion (space portion) of the third catalyst layer, the amount of the phosphorus compound deposited on the downstream portion of the third catalyst layer is reduced, The effect on the activity of the catalyst component is reduced and the catalyst has a high purification ability when considered as a whole. The phosphorus compound is, for example, 50 g or less, preferably 30 g or less, more effectively 15 g or less, and most effectively, per liter of a carrier (for example, a three-dimensional structure) in terms of phosphorus oxide (P ₂ O ₅ ). In a state where 10 g or less is accumulated, a considerable amount of the phosphorus compound is deposited in the upstream portion of the third catalyst layer and the intermediate portion (space portion), so that the catalyst component in the downstream portion of the third catalyst layer is The effect on the activity is reduced and the catalyst has a high purification ability when considered as a whole.

(Phosphorus compound)
As a phosphorus compound causing phosphorus poisoning, for example, zinc dialkyldithiophosphate and the like are known. The catalyst of the present invention is particularly useful for purifying exhaust gas from a gasoline engine using a lubricant containing a phosphorus compound.

  Further, when the catalyst layer is used by coating it on the refractory three-dimensional structure, generally, the phosphorus compound is deposited at a high concentration on the surface of the catalyst layer, and the phosphorus compound is deposited in the depth direction inside the catalyst layer. The concentration distribution is skewed. The concentration is lower as approaching the three-dimensional structure, and higher as approaching the outermost surface of the coat layer in contact with the gas layer. On the other hand, the concentration distribution of the phosphorus compound in the flow direction of the exhaust gas is also skewed. Generally, the concentration of the phosphorus compound is higher nearer to the inflow-side end face, and lower when closer to the outflow-side end face. There is no specific increase in concentration between the end face and the outflow end face. However, in the catalyst of the present invention, since the intermediate portion having the desired length and thickness is provided at a desired position in the exhaust gas flow direction, the amount of the phosphorus compound deposited at the position having the intermediate portion is less than the intermediate portion. It is deposited more than in the case where it is not provided.

  The distribution of the phosphorus compound deposited on the catalyst layer in the exhaust gas flow direction can be analyzed using a method such as XRF (X-ray fluorescence analysis). Further, the concentration distribution of the phosphorus compound in the depth direction inside the catalyst layer can be obtained by analyzing a mapping image analyzed in a spectrum belonging to a P (phosphorus) Kα ray by an EPMA (electron probe microanalyzer) analysis. . The same analysis can be performed using SEM-EDX or the like.

  The present invention has been described above by showing preferred embodiments for easy understanding. Hereinafter, the present invention will be described based on examples. However, the above description and the following examples are provided for illustrative purposes only, and are not provided for the purpose of limiting the present invention. Accordingly, the scope of the present invention is not limited to the embodiments or examples specifically described herein, but only by the claims.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not construed as being limited to these examples, and examples obtained by appropriately combining technical means disclosed in each example are not limited thereto. It is intended to be included in the scope of the invention.

(Example 1) A manufacturing method of palladium nitrate aqueous solution of a _catalyst, CeO 2 -ZrO ₂ composite oxide, aluminum oxide _{(Al 2 O} 3), barium sulfate and lanthanum acetate, the mass ratio of palladium _(Pd): CeO 2 -ZrO ₂ Composite oxide: Al ₂ O ₃ : barium sulfate (BaSO ₄ ): lanthanum oxide (La ₂ O ₃ ), each being weighed so as to be 3.54: 38: 38: 10: 0.4 in terms of conversion. And water, and wet-pulverized with a ball mill to prepare a slurry a0.

Next, as a refractory three-dimensional structure, a cell having a diameter of 118.4 mm, a length of 91 mm, a cylindrical shape of 1.0 L, 600 cells per square inch (6.45 cm ² ), and a cell wall thickness of 3.5 mil (0.0889 mm) were used. The slurry a0 was wash-coated from the upstream end face onto the cordierite carrier of (2) such that the length of the first catalyst layer shown in Table 1 and the amount of Pd carried after firing became the amount shown in Table 2. After drying at 150 ° C. for 15 minutes, it was baked at 550 ° C. for 30 minutes to obtain an intermediate product A1 having a first catalyst layer provided on a refractory three-dimensional structure.

Next, the intermediate product A1 was wash-coated with the slurry a0 from the downstream end face so that the length of the second catalyst layer shown in Table 1 and the supported amount after firing became the amount shown in Table 2, and dried in the same manner. Thereafter, calcination was performed to obtain an intermediate product A2 provided with the first catalyst layer and the second catalyst layer. The intermediate product A2, when the measurement of the intermediate portion of the length L ₂ by calipers were shown in Table 1.

Next, a rhodium nitrate aqueous solution, a palladium nitrate aqueous solution, a CeO ₂ —ZrO ₂ composite oxide, aluminum oxide and lanthanum oxide were mixed at a mass ratio of Rh: Pd: CeO ₂ —ZrO ₂ composite oxide: Al ₂ O ₃ : La ₂ Each was weighed so as to be 0.225: 0.14: 47: 60: 0.8 in terms of O ₃ , mixed with water, and wet-ground with a ball mill to obtain a slurry a3.

The prepared slurry a3 was converted into an intermediate product A2, and the supported amount after calcination in terms of Rh, Pd, CeO ₂ -ZrO ₂ composite oxide, Al ₂ O ₃ , BaSO ₄ , and La ₂ O ₃ was 108 g per liter of the carrier. Wash coat was performed from the upstream side to the downstream side of the catalyst so as to form a first catalyst layer, a second catalyst layer, and a third catalyst layer by similarly drying at 150 ° C. for 15 minutes and then baking at 550 ° C. for 30 minutes. Catalyst A was obtained.

(Example 2)
A catalyst B was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 3)
A catalyst C was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 4)
A catalyst D was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 5)
A catalyst E was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Comparative Example 1)
The same carrier was coated with the slurry a0 to have the length shown in Table 1 to obtain an intermediate product F1. Next, the slurry a0 is continuously wash-coated so as not to form an intermediate portion on the intermediate product F1 from the downstream end face, dried and fired in the same manner, and provided with the first catalyst layer and the second catalyst layer. F2 was obtained. It was confirmed that there was no intermediate part for the intermediate product F2.

  Next, the intermediate product F2 was wash-coated with the slurry a3 from the upstream side to the downstream side of the catalyst so that the carried amount after calcination was 108 g per liter of the carrier. I got

(Example 6)
A catalyst G was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 7)
A catalyst H was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 8)
A catalyst I was produced in the same manner as the catalyst A, except that the coating was performed so as to have the length shown in Table 1 and the amount of the noble metal shown in Table 2.

(Example 9)
An aqueous solution of palladium nitrate, CeO ₂ -ZrO ₂ composite oxide, aluminum oxide (Al ₂ O ₃ ), barium sulfate and lanthanum acetate were mixed at a mass ratio of Pd: CeO ₂ -ZrO ₂ composite oxide: Al ₂ O ₃ : BaSO ₄ : It is weighed so that it becomes 1.18: 14.07: 14.07: 3.7: 0.15 in terms of La ₂ O ₃ , and the components other than the noble metal are mixed by wet pulverization to obtain a slurry a0. The same slurry j1 was prepared.

Next, a palladium nitrate aqueous solution, CeO ₂ —ZrO ₂ composite oxide, aluminum oxide (Al ₂ O ₃ ), barium sulfate, and lanthanum acetate were mixed at a mass ratio of Pd: CeO ₂ —ZrO ₂ composite oxide: Al ₂ O ₃ : BaSO ₄ : La ₂ O ₃ : 2.36: 23.93: 23.93: 6.3: 0.25 in terms of conversion, and the ratio of components other than noble metal by wet pulverization. Produced the same slurry j2 as the slurry a0. An intermediate product J1 was obtained by wash-coating the slurry k1 in the same manner as when preparing the catalyst A, and then an intermediate product J2 was obtained by wash-coating the slurry j2. Similarly, the obtained intermediate product J2 is wash-coated with the slurry a3 from the upstream side to the downstream side of the catalyst so that the carried amount after calcination becomes 108 g per 1 liter of the carrier. , A catalyst J provided with a second catalyst layer and a third catalyst layer.

(Example 10)
A catalyst K was produced in the same manner as the catalyst J, except that the coating was performed so that the amount of the noble metal was as shown in Table 2.

(Example 11)
A catalyst L was produced in the same manner as the catalyst J, except that the amount of the noble metal shown in Table 2 was applied.

(Example 12)
A catalyst M was produced in the same manner as the catalyst J, except that the coating was performed so that the amount of the noble metal was as shown in Table 2.

(Comparative Example 2)
The slurry a0 was wash-coated from the upstream end face to the downstream end face so that the supported amount after firing on the same carrier as the catalyst A was 89.9 g per liter of the carrier, and dried at 150 ° C. for 15 minutes. It was baked at 550 ° C. for 30 minutes to obtain an intermediate product N1.

  Next, the slurry a3 was wash-coated on the intermediate product N1 in the same manner as when the catalyst A was prepared, and then dried and fired to obtain a catalyst N without a second catalyst layer and an intermediate portion.

  Table 1 shows the ratio of the start position of the first catalyst layer and the intermediate portion to the entire length of the catalyst, the length of the intermediate portion of the third catalyst layer, the ratio of the length of the intermediate portion to the entire length of the catalyst, and the length of the second catalyst layer. Was.

  Note that the catalyst F and the catalyst N were not provided with an intermediate portion.

  The amount of Pd and Rh carried in the first catalyst layer, the second catalyst layer, and the third catalyst layer [g / L], and the amount of the noble metal in the first catalyst layer and the second catalyst layer in the first catalyst layer Table 2 shows the noble metal content [%].

H ₃ , H ₄ , and H ₅ of each catalyst were measured with a 3D microscope. In addition, the ratio of H _{4 to} H ₃ [%], the ratio of H _{4 to} H ₅ [%], and the ratio of H _{5 to} H ₃ [%] were calculated. The results were as shown in Table 3.

<Heat endurance test>
Each of the catalysts obtained in the above production examples was placed downstream of the 3.0 L engine, and the temperature of the catalyst bed was set to 940 ° C. The engine was a gasoline engine. A cycle in which the A / F at the catalyst inlet was stoichiometric, rich, and the fuel supply was stopped was repeatedly operated for a total of 66 hours to perform a heat durability test.

Next, each of the heat-treated catalysts was installed downstream of the exhaust port of the 3.0 L engine, and the temperature of the catalyst bed was adjusted to 740 ° C. using oil having a phosphorus (P) concentration of 3000 ppm in engine oil. By operating for an hour, phosphorus poisoning treatment was performed. By analyzing the phosphorus content of each of the endured catalysts by XRF, 7.5 g of a phosphorus compound as phosphorus oxide (P ₂ O ₅ ) per liter of a carrier (for example, a three-dimensional structure) is used as a catalyst. It was confirmed that it was contained.

<Amount of phosphorus compound attached to exhaust gas purification catalyst>
For the catalysts D, F, G and H having a length of the first catalyst layer of 40 mm, the distribution of the attached amount of phosphorus was examined. With respect to the catalysts B and E which have been subjected to the phosphorus poisoning, the respective catalysts are cut at positions of 40 mm, 45 mm, 50 mm, 55 mm, and 60 mm in the outflow direction with the end face of the exhaust gas inflow side being 0 mm (in Table 4 below, denoted sites less 45mm or 40mm and 40-45Mm, denoted similarly for the other sites), phosphorus compound content deposited on each part of the downstream side from 40mm to _(P 2 _{O 5} equivalent) examined by XRF analysis Was. Table 4 shows the deposition distribution [%] of the phosphorus compound obtained by dividing the amount of the phosphorus compound contained in each part from 40 mm to 91 mm by the total amount of the phosphorus compound contained in each part downstream from 40 mm.

  From Table 4, it can be seen that the catalyst F having no intermediate portion has a decreasing phosphorus compound deposition rate from the upstream side to the downstream side, whereas the catalysts G, D and H having the intermediate portion have the intermediate portion or the intermediate portion. It can be seen that the phosphorus compound is deposited specifically at a high level on the downstream side of. For example, in the case of the catalyst G, the deposited phosphorus is 38 at 40-45 mm where there is an intermediate portion, and 21 at other portions (45-50 mm), and many phosphorus compounds are detected in the intermediate portion. The catalyst D has a diameter of 37 at 45-50 mm downstream of the intermediate portion and a diameter of 16 at another portion (50-55 mm). The catalyst H is 35 at 50-55 mm on the downstream side of the intermediate portion, 5 at 55-60 mm on the downstream side, and 25 at 40-45 mm on the upstream side, and the intermediate portion has another portion. Excessively more phosphorus is deposited. On the other hand, in the case of the catalyst F having no intermediate portion, the amount of phosphorus accumulated on the upstream side of the catalyst, which first contacts the exhaust gas, is large, and the amount of accumulated phosphorus is small on the downstream side of the catalyst. From these results, a large amount of the phosphorus compound was detected at the intermediate portion or at the downstream side of the intermediate portion, and the deposition of the phosphorus compound at the site downstream of the intermediate portion was suppressed. Phosphorus poisoning in the first catalyst layer and the second catalyst layer containing a large amount of catalyst components and the third catalyst layer portion laminated thereon can be suppressed.

<Performance evaluation of exhaust gas purification catalyst>
Each of the catalysts after the heat treatment was placed downstream of the 2.0 L engine, and the temperature was stabilized at 100 ° C., and then the exhaust gas temperature at the catalyst inlet was raised from 100 ° C. to 500 ° C. The engine was a gasoline engine. The gas discharged from the catalyst outlet was sampled, and the respective purification rates of CO, THC and NOx were calculated. After starting the temperature increase, the temperature at which each purification rate reached 50% was defined as T50, and the time required to reach T50 was examined.

(Effect of the starting position of the middle part)
Further, for the catalysts A to E, the ratio of the position where the intermediate portion starts to the total length of the catalyst was calculated by the following equation.

L ₁ ÷ L × 100
FIG. 2 is a graph in which the calculated ratio [%] is plotted on the horizontal axis, where the ratio of the intermediate portion start position to the entire catalyst length is plotted, and the time to reach T50 [seconds] is plotted on the vertical axis. From FIG. 2, it was found that the catalyst of the example had a shorter time to reach T50 than the catalyst of the comparative example, and that the exhaust gas purification occurred quickly.

(Effect of the length of the middle part)
The effect of the length of the middle part was evaluated in a similar manner. For each of the catalysts D, F, G, H and I having the same starting position in the intermediate portion and different lengths of the intermediate portion, the time to reach T50 was measured. FIG. 3 is a graph in which the ratio [%] of the length of the intermediate portion to the total length of the catalyst is plotted on the horizontal axis, and the time [sec] until T50 is plotted on the vertical axis.

  As shown in FIG. 3, it was found that the catalyst of the example had a shorter time to reach T50 than the catalyst of the comparative example, and the exhaust gas purification occurred quickly.

(Effect of precious metal distribution)
The effect of precious metal distribution was evaluated in the same way. The time to reach T50 was measured for each of the catalysts C, J, K, L and M having the same starting position and the same length of the middle portion and different noble metal distributions. FIG. 4 is a graph in which the ratio of the amount of the noble metal contained in the first catalyst layer [%] to the total amount of the noble metal in the first catalyst layer and the second catalyst layer [%] is plotted on the horizontal axis, and the time to reach T50 [sec] is plotted on the vertical axis. Shown as 4.

  It was found that the concentration of palladium contained in the first catalyst layer (upstream of the exhaust gas) of the catalyst of the example was shorter in the time required to reach T50 than that of the catalyst of the comparative example, and that the exhaust gas purification occurred quickly.

  For the catalysts N and C containing palladium contained in the second catalyst layer in the first catalyst layer and having no intermediate portion, the time to reach T50 was evaluated by the same method. The time to reach T50 is shown in FIG.

  As described above, the present invention has been exemplified by the preferred embodiments of the present invention, but it is understood that the scope of the present invention should be interpreted only by the appended claims. Patents, patent applications, and other references cited herein are to be incorporated by reference in their entirety, as though the contents themselves were specifically described herein. It is understood that.

  The exhaust gas purifying catalyst according to the present invention can efficiently purify exhaust gas from an internal combustion engine even after long-term use. Therefore, it can be widely applied to all industries using an internal combustion engine, for example, automobiles, railways, ships, aviation, various industrial machines, and the like. The catalyst of the present invention is useful for purifying exhaust gas from a gasoline engine, and is particularly useful for purifying exhaust gas from a gasoline engine using a phosphorus compound as a lubricant.

Claims (9)

A catalyst for purifying exhaust gas, comprising a carrier, a first catalyst layer on an upstream side, a second catalyst layer on a downstream side, and a third catalyst layer,
An upstream portion of the third catalyst layer is on the first catalyst layer;
A downstream portion of the third catalyst layer is on the second catalyst layer;
An intermediate portion of the third catalyst layer between the upstream portion and the downstream portion exists between the first catalyst layer and the second catalyst layer;
Exhaust gas purification catalyst. The thickness H ₄ of the intermediate portion is characterized thinner than the thickness H ₅ having a thickness of H ₃ and the downstream portion of the upstream portion catalyst of claim 1.   3. The catalyst according to claim 1, wherein a ratio of a length of the first catalyst layer to a total length of the catalyst is 10% to 70%. 4.   The catalyst according to any one of claims 1 to 3, wherein a ratio of a length of an intermediate portion of the third catalyst layer to a total length of the catalyst is 1% to 25%.   The first catalyst layer, the second catalyst layer, and the third catalyst layer all contain a noble metal, and the mass of the noble metal contained in the first catalyst layer is larger than the mass of the noble metal contained in the second catalyst layer. The catalyst according to any one of claims 1 to 4, wherein the amount is large.   The catalyst according to any one of claims 1 to 5, wherein the third catalyst layer includes rhodium and palladium, and the first catalyst layer and the second catalyst layer include palladium.   The catalyst according to any one of claims 1 to 6, wherein the first catalyst layer, the second catalyst layer, and the third catalyst layer contain cerium.   The catalyst according to any one of claims 1 to 7, which is used for purifying an exhaust gas containing a phosphorus compound.   A method for purifying exhaust gas, comprising a step of bringing exhaust gas into contact with the catalyst according to any one of claims 1 to 8.